The present invention generally relates to vehicle suspensions. More particularly, the present invention relates to elastomeric spring vehicle suspensions for use in vocational or heavy haul truck applications.
Elastomeric spring vehicle suspensions for use in vocational or heavy haul truck applications are known. Such suspensions may be classified as single spring rate suspensions or variable spring rate suspensions.
Single spring rate suspensions have a fixed spring rate that generally must be set at a level that produces a suspension with either a comfortable ride or a stiff suspension exhibiting adequate roll stability. As a result, either roll stability or ride quality is compromised in single spring rate suspensions, depending upon the selected spring rate.
Variable rate suspensions overcome this deficiency of single rate suspensions by providing for multiple spring rates during operation. As the sprung load is increased, the spring rate is correspondingly increased.
An example of a variable spring rate elastomeric spring suspension for use in vocational or heavy haul truck applications is disclosed in U.S. Pat. No. 6,585,286, the disclosure of which is hereby incorporated herein by reference. That suspension utilizes bolster springs and auxiliary springs to achieve its variable spring rate.
The spring rate for such a suspension can change due to the engagement or disengagement of the auxiliary spring as a function of load. The ride quality of a lightly loaded chassis having such a suspension is quite good without sacrificing roll stability at rated chassis load. When a lightly to moderately loaded chassis with such a suspension encounters moderate to large variations in roadway or operating conditions, frequent engagement and disengagement of the auxiliary spring may occur. For each such engagement or disengagement of the auxiliary spring, the spring rate for the system may undergo an abrupt change known as strike-through effect. Ride quality may be compromised as a result. Graphically, the spring rate has a discontinuity at the load where the auxiliary spring is engaged or disengaged and represents a step function.
Prior elastomeric spring suspensions for vocational or heavy haul truck applications require their elastomeric springs to undergo loading that is compressive, tensile and/or shearing in nature. Tensile loading causes elastomeric break down.
In view of the conditions identified above with respect to prior elastomeric spring vehicle suspensions for vocational or heavy haul truck applications, it is desired to develop a new and improved suspension of that type for those applications.
Accordingly, it is desired to develop elastomeric spring vocational suspensions that have a continuously increasing spring rate (curvilinear and with no discontinuities) as a function of load.
It is desired to develop elastomeric spring vocational suspensions that have an almost linearly increasing spring rate as a function of load.
It is desired to develop elastomeric spring vocational suspensions that provide good ride quality on a lightly loaded chassis without sacrificing roll stability at rated chassis load.
It is also desired to develop elastomeric spring vocational suspensions that do not experience any abrupt change in spring rate due to engagement or disengagement of an auxiliary spring as the vehicle encounters moderate to large variations in roadway or operating conditions.
It is further desired to develop elastomeric spring vocational suspensions having springs that do not undergo tensile loading.
It is still further desired to develop elastomeric spring vocational suspensions having no tire chain usage restrictions, as is the case with many elastomeric spring vocational suspensions.
It is also desired to develop elastomeric spring vocational suspensions having minimal interaxle brake load transfer due to the pivot point created at the equalizing beam center bushing.
It is further desired to develop elastomeric spring vocational suspensions having improved articulation by virtue of the pivot point created at the equalizing beam center bushing.
It is still further desired to develop elastomeric spring vocational suspensions having improved durability due to reduced number of fasteners, mechanical joints that reduce the criticality of fastener preloads, and the aforementioned elimination of tensile loading in elastomeric springs.
It is further desired to develop a modular suspension.
Vocational suspensions designed in accordance with the principles of those disclosed herein may achieve these benefits. These and other desired benefits of the preferred forms of the invention will be apparent from the following description. It will be understood, however, that a suspension could still appropriate the claimed invention without accomplishing each and every one of the desired benefits, including those gleaned from the following description. The appended claims, not these desired benefits, define the subject matter of the invention. Any and all benefits are derived from the preferred forms of the invention, not necessarily the invention in general.